Fluidic switching circuits

ABSTRACT

The invention relates to a fluid pressure-ratio switching circuit which provides an output only when one of a pair of independent control signals is greater than the other. Switching is effected in a bistable fluidic device, one or both of the outputs of which are used to provide control signals for two subsequent stages of amplification. Amplification is effected by a pair of fluidic proportional amplifier devices, the arrangement being that the circuit output is taken from the vent port of the final amplifier device.

United States Patent lnventor Ronald Alfred Heath Harborne, England Appl. No. 859,740 Filed Sept. 22, 1969 Patented Oct. 19, 1971 Assignee Joseph Lucas (Industries) Limited Birmingham, England Priority Sept. 30, 1968 Great Britain 46266/68 FLUIDIC SWITCHING CIRCUITS 6 Claims, 2 Drawing Figs.

US. Cl 137/81.5, 235/200 Int. Cl Fl5c 1/12 Field of Search 137/81.5', 235/201, 200

[56] References Cited UNITED STATES PATENTS 3,338,515 8/1967 Dexter 137/81.5 X 3,339,571 9/1967 Hatch, Jr. 137/81.5 3,409,032 11/1968 Boothe et al 137/81.5 X 3,443,574 5/1969 Posingies.... 137/81.5 3,457,847 7/1969 Furlong l37/81.5 X 3,458,129 7/1969 Woodson 137/81.5 X 3,494,357 2/1970 Kimball l37/81.5 X

Primary Examiner-Samuel Scott AttorneyI-I0lman & Stern ABSTRACT: The invention relates to a fluid pressure-ratio switching circuit which provides an output only when one of a pair of independent control signals is greater than the other. Switching is effected in a bistable fluidic device, one or both of the outputs of which are used to provide control signals for two subsequent stages of amplification. Amplification is effected by a pair of fluidic proportional amplifier devices, the arrangement being that the circuit output is taken from the vent port of the final amplifier device.

PATENTED BT 1 l 3,613,705

7%ZIJNV Ti mwms FLUIDIC SWITCHING CIRCUITS This invention relates to a fluidic switching circuit.

The circuit makes use of two basic types of fluidic devices. The first of these (hereinafter called a bistable fluidic device) has an inlet port, a pair of outlet ports and a pair of control ports. The device operates on the known wall attachment effect and is such that the supply of pressure to either control port prevents wall attachment in the region of that port to cause flow from one outlet port at a proportion of the inlet pressure. The device is bistable in that once flow from either outlet port has been established such flow will continue until pressure is applied to the other control port to switch over the flow. The device also has a dump port through which the outlet port which, at any time, is not receiving the through flow is vented.

The other type of device used is referred to hereinafter as a proportional amplifier device and comprises an inlet port through which fluid enters the device and emerges through a nozzle into a vented chamber from which two outlet ports diverge. Two control ports open into opposite sides of the vented chamber and the device is such that the pressures at the two outlet ports are continuously variable with the ratio of the pressures at the two inlet ports. The pressure at each outlet port is dependent on the ratio of the control port pressures, the arrangement being such that when the control port pressures are equal substantially the whole of the fluid issues from a vent port in the chamber.

A fluidic switch circuit in accordance with the invention comprises a bistable fluidic device with its control ports connected respectively to a pair of independent signal pressure sources, a first fluidic proportional amplifier device with its inlet port connected to a supply pressure source and at least one of its control ports connected to one of the outlet ports of the bistable device and a second fluidic proportional amplifier device with its inlet port connected to the supply pressure source and its control ports connected respectively to the outlet ports of the first fluidic proportional amplifier device, the arrangement being such that when the bistable device is in one of its stable states an output'signal pressure is derived from the vent port of the second fluidic proportional amplifier device.

Two examples of the invention are illustrated diagrammatically in the accompanying drawings.

FIG. 1 shows a circuit comprising a bistable fluidic device 10, a first fluidic proportional amplifier device 11 and a second fluidic proportional amplifier device 12. One of the control ports 13 of the device is connected to a first signal pressure source P, and the inlet port 14 and the other control ports 15 are connected to a second signal pressure source P The pressures P, and P are independently variable. The outlet port 16 from which fluid issues when the pressure at port P, is in excess of the pressure at port P is vented to atmosphere. The other outlet port 17 provides the output of the device 10.

The device 11 has its inlet port-l8 connected to a supply pressure source P. One control port 19 is connected to the outlet 17 of device 10, the other control port 20 being open to atmosphere. The device has outlet ports 21, the pressure at which increases with increasing pressure at port 19, and 22 the pressure at which increases with decreasing pressure at port 19.

The device 12 has its inlet port 23 connected to the supply source P and its control ports 24, 25 connected respectively to the outlet ports 21, 22 of the device 11. The outlet ports 26, 27 of the device 12 are left open to atmosphere but the vent port 28 provides the outlet connection of the circuit.

in use, whenever P, is less than P device It] delivers flow from the port 17 so that an amplified signal is provided from ort 21 of the device 11. The output of device 12 is therefore from the port 26 and the pressure P, at the vent port 28 will therefore be low. When P, exceeds P on the other hand, port 17 of device 10 is vented so that both of the ports 19, 20 of the device II are, in effect, at the same pressure and therefore ports 21 and 22 are at the same pressure. The pressure P at port 28 therefore rises to a maximum.

proportional amplifiers have an inherent asymmetry, due to manufacturing tolerances. Equal pressures applied to the control ports of a proportional amplifier will therefore not necessarily result in a maximum recovery of fluid at the vent port, some of the fluid being routed to one of the outlet ports. For maximum recovery at the vent port, therefore, the control pressures must be unequal by some amount, and this amount is also dependent on the pressure of the fluid supplied to the inlet port. Flow restrictors may be introduced into the circuit to control the supply pressure and to set an input pressure differential to ensure maximum recovery at the vent port.

FIG. 2 shows a circuit incorporating flow restrictors, the devices 10, 11 and 12 being used as before. ln this case, however, the port 16 of the device 10 is also connected to the port 20 of device 11. In the connections between port 17 and port 19 and between ports 16 and port 20 flow restrictors 29, 30 are employed. Similarly flow restrictors 31, 32 are employed in the connections between the ports 22 and 25 and between the ports 21 and 24. Further flow restrictors 33, 34 are present in the connections between the source P and the port 18 and 23 respectively. As before, when P, is less than P the output of the device 12 is from the port 26, and when P, is greater than P the output is from the vent port 28. Adjustment of the flow restrictors 29 to 34 is such that when P, is less than P there is a sufficient pressure at control port 24 to produce a maximum delivery at port 26, and also that when P, exceeds P the pressures at the ports 24, 25 are such as to produce a maximum recovery pressure at the port 28. Restrictors 29, 32 will thus permit relatively large flows and restrictor 30 a small flow. Restrictor 31 will be balanced against restrictor 32 for a maximum recovery at port 28.

It is to be noted that the ambient pressure around each fluidic device in each case may be maintained at a level other than the existing atmospheric pressure. This can result in better switching of the bistable devices with the result that higher pressures are passed from the outlet ports to the control ports of the devices in the following stage or stages.

Having thus described my invention what I claim as new and desire to secure by Letters Patent is:

1. A fluid switch circuit comprising a bistable fluidic device with its control ports connected respectively to a pair of independent signal pressure sources, a first fluidic proportional amplifier device with its inlet port connected to a supply pres sure source and at least one of its control ports connect to one of the outlet ports of the bistable device and a second fluidic proportional amplifier device including a pair of outlet ports connected to atmosphere and a vent port, said second amplifier having its inlet port connected to the supply pressure source and its control ports connected respectively to the outlet ports of the first fluidic proportional amplifier device, the arrangement being such that when the bistable device is in one of its stable states an output signal pressure is derived from the vent port of the second fluidic proportional amplifier device.

2. A circuit as claimed in claim 1 in which the inlet of the bistable device is connected to one of the signal pressures.

3. A circuit as claimed in claim 1 in which each of the control ports of the first proportional amplifier device is connected to a respective one of the outlet ports of the bistable device.

4. A circuit as claimed in claim 3 which includes a flow restrictor in each of the connections from the control ports of the first proportional amplifier to the outlet ports of the bistable device.

5. A circuit as claimed in claim 3 which includes a flow restrictor in each of the connections from the control ports of the second proportional amplifier to the outlet ports of the first proportional amplifier.

6. A circuit as claimed in claim 3 which includes a flow restrictor in each of the supply pressure connections to the inlet ports of the first and second proportional amplifiers respectively. 

1. A fluid switch circuit comprising a bistable fluidic device with its control ports connected respectively to a pair of independent signal pressure sources, a first fluidic proportional amplifier device with its inlet port connected to a supply pressure source and at least one of its control ports connect to one of the outlet ports of the bistable device and a second fluidic proportional amplifier device including a pair of outlet ports connected to atmosphere and a vent port, said second amplifier having its inlet port connected to the supply pressure source and its control ports connected respectively to the outlet ports of the first fluidic proportional amplifier device, the arrangement being such that when the bistable device is in one of its stable states an output signal pressure is derived from the vent port of the second fluidic proportional amplifier device.
 2. A circuit as claimed in claim 1 in which the inlet of the bistable device is connected to one of the signal pressures.
 3. A circuit as claimed in claim 1 in which each of the control ports of the first proportional amplifier device is connected to a respective one of the outlet ports of the bistable device.
 4. A circuit as claimed in claim 3 which includes a flow restrictor in each of the connections from the control ports of the first proportional amplifier to the outlet ports of the bistable device.
 5. A circuit as claimed in claim 3 which includes a flow restrictor in each of the connections from the control ports of the second proportional amplifier to the outlet ports of the first proportional amplifier.
 6. A circuit as claimed in claim 3 which includes a flow restrictor in each of the supply pressure connections to the inlet ports of the first and second proportional amplifiers respectively. 